In co-ordinate measuring machines, an object is measured by relative motion of a probe and an object in a controlled manner, usually from a datum, until a "touch" on the object is indicated by the probe or the probe is displaced by an indicated amount. The co-ordinates of the touch position are recorded or the probe indication combined with the machine indication. By repeated such actions the dimensions of the object can be determined. Appropriate actions are carried out with probes in machine tools, robot and similar machines.
UK Patent Application 8815984.3, published as GB-A-2220748, describes a touch probe for taking two dimensional measurements which can be mounted on a suitable kinematic mounting, to be movable to make measurements in the third dimension. However, the mounting is expensive and bulky.
The use of a cone of light emitted from a fibre optic and reflected by a plane mirror to an array of receiver fibre optics has been proposed (EP A 0429378--CNRS/CEMAGREF) for force measurement by the determination of the direction and amplitude of small lateral displacements of the mirror when the mirror is mounted to be responsive to an applied force, e.g. in an anemometer, by fluid flow or in a "joy-stick". In this arrangement only a part of the divergent cone of light is incident on the deflected mirror and the greater the defection the less light is so-incident. Furthermore the reflected light continues to diverge so that some of the already-reduced light misses the fibre receiver array while that reaching the array is of reduced intensity, due to the continued divergence.
Another form of three-dimensional probe for displacement indication is based on three small grating scales but this also is bulky, complex and expensive.